(1) Field of the Invention
The present invention relates generally to the displaying of data files, and more particularly to a method of displaying time series data on a finite resolution display device that is part of an interactive computer system where it is desirable to minimize the time required to display a portion of a data file.
(2) Description of the Prior Art
The graphing or plotting of large data files (e.g., time sampled data) on a display device (e.g., CRT screen, printer, etc.) is typically governed by the finite resolution of the display device. The resolution of the display device is defined by the display device's indivisible unit of display. For example, a CRT screen's resolution is expressed in pixels. Thus, if the resolution of a CRT screen is 1000.times.700 pixels and each column of pixels represents, for example, one instant in time, then only 1000 instants in time can be displayed at once. Since large data files typically contain more than 1000 data points, the data file must be compressed in order to be completely viewed on the CRT screen.
In terms of displaying time sampled data on a CRT screen, each column of pixels is "overplotted" with a number of data points from the data file in order to compress the data file with respect to time. Accordingly, much of the data is ignored or printed redundantly at the same column on the CRT screen. If it is necessary to display just a small portion of the data, i.e., "zoom in" fewer data points are used to overplot a column of pixels. However, the entire data file must still be processed. Since the transfer of large data files from a memory device to a display device is slow, each requested "zoom in" or "zoom out" causes a time delay at the display device. Such time delays are undesirable/unacceptable when it comes to interactive systems where an operator needs to zoom in and out on the data in order to analyze same.